The present invention relates to devices and methods for delivering or administering substances and, more particularly, to an administering apparatus for administering an injectable substance or product in selected amounts or doses. The administering apparatus can, in particular, be an injection apparatus, for example an injection pen, such as may be used in many different therapies, for example in diabetes therapy or in administering growth hormone.
Administering apparatus, for example, injection pens, which allow a product or substance dosage to be administered to be selected typically comprise a so-called dosing mechanism which protrudes from a casing opening of the administering apparatus. The dosing mechanism may be button-like, generally similar to the activating button of a ballpoint pen. In order to prepare for the delivery or administration of a substance, the product dosage may be selected by rotating the dosing button relative to the casing. The rotational dosing movement pre-sets a conveying means. For administering, the dosing button is then pressed, from its dosage selection position, a little way into the casing, as far as a front end position. This activates the pre-set conveying means. The conveying means acts on the product or substance contained in a reservoir of the administering apparatus and conveys the selected product dosage, i.e., the product dosage is delivered from the reservoir. In the front end position, the dosing mechanism is blocked against a reverse movement. After the blocking engagement is released, the dosing button is automatically moved back to the dosage selection position and the administering apparatus is ready to administer another dose and, as applicable in some devices, also to select the dosage anew.
Administering apparatus of the type cited above are known, for example, from WO 99/03522 and EP 0 897 728 A1. In the this type of device, however, in order to increase dosing reliability, the reverse movement of the dosing button back to the dosage selection position is only possible if, in the front end position of the dosing button, a dosage indicator of the administering apparatus has been reset to “zero”. In these apparatus, the dosage is indicated mechanically with the aid of a dosage indicator sleeve. During the dosing movement of the dosing button, the dosage indicator sleeve is also moved relative to the casing. The position of the dosage indicator sleeve relative to the casing is used to indicate the selected product dosage. In the administering apparatus of EP 0 897 728 A1, two dosage indicator sleeve are required for indicating the selected product dosage, namely, one dosage indicator sleeve for indicating individual dosage units and another dosage indicator sleeve for indicating the dosage units in increments of ten.
In order to reset the dosing button after the product dosage has been administered, the administering apparatus of WO 99/03522 requires two hand operations to be performed: one in order to move the dosage indicator sleeve back to its zero-dosage position and, two, to release a blocking engagement which can only be released in the zero-dosage position of the dosage indicator sleeve. In the administering apparatus of EP 0 897 728 A1, the dosing button is automatically moved back or reset after the two dosage indicator sleeves have been moved back to their zero-dosage position. For the dosing button to be automatically reset by resetting the dosage indicator alone, the dosage indicator sleeve of the two dosage indicator sleeves, which indicate the dosage in increments of ten (the decimal dosage indicator sleeve), is provided with an axial groove. This decimal dosage indicator sleeve surrounds a blocking member which comprises a spring-elastic tongue which is pressed radially inwards by the decimal dosage indicator sleeve into a blocking engagement in which the spring-elastic tongue blocks the resetting movement of the dosing button. If, however, the decimal dosage indicator sleeve is moved to the zero-dosage position, then its axial groove overlaps the spring tongue of the blocking member and the spring tongue can pre-latch radially outwards into the axial groove of the decimal dosage indicator sleeve due to its inherent elasticity force. This pre-latching releases the blocking engagement and the dosing button is automatically moved back to its dosage selection position, driven by the spring force. This resetting mechanism may be susceptible to faults.